The present invention relates to a method of alignment between a mask and a semiconductor wafer and, more particularly to a method of alignment between a mask and a semiconductor wafer by detecting misalignment therebetween in an X-ray lithography apparatus.
To form a fine pattern on a semiconductor wafer a precise alignment between the mask and the semiconductor wafer is necessary. As a prior art, there is an optical alignment method which employs a linear Fresnel zones plate lens (hereinafter called as LFZP) proposed by Bernard Fay et al. in U.S. Pat. No. 4,311,389 and in "Journal of Vacuum Science Technology" Vol. 16(6), Nov./Dec., 1979 pp. 1954-1958 entitled "Optical alignment system for submicron X-ray lithography".
In the conventional method, a LFZP as a lens for a monochromatic radiation such as a laser beam is formed at a peripheral portion of the mask, and a reflecting grating pattern is formed at a peripheral portion of the semiconductor wafer such that it is positioned under the LFZP of the mask in the lithography process. A parallel laser beam is irradiated to the LFZP on the mask and focused on the semiconductor wafer to detect whether the reflecting grating pattern on the semiconductor wafer is positioned under the center of the LFZP or not. More particularly, the parallel laser beam in the prior art is changed in its incidence angle by a oscillating mirror to scan the focused portion on the wafer thereby examining the position of the reflecting grating pattern. When the reflecting grating pattern is not positioned under the center of the LFZP, that is, misalignment is detected, the semiconductor wafer or the mask is horizontally moved automatically so as to position the reflecting grating pattern of the semiconductor just under the center of the LFZP of the mask.
The above-described conventional method of alignment between a mask and a wafer, however, requires an optical system which includes the oscillating mirror and two lenses and therefore the prior art suffers from the disadvantages that the apparatus is complicated, it is difficult to reduce the size of the apparatus, and the cost is high. Further, since a signal from a detector and the oscillating mirror driving signal are subjected to phase detection to obtain a misalignment signal, the response time for the misalignment signal is determined by the frequency of the oscillating mirror, resulting in a disadvantageously, low response speed for detecting alignment condition.